Numerous animal studies utilizing morphological techniques have indicated prefusion alterations in the palatal shelf epithelium during palatogenesis. Such alterations are highly localized to those areas which will fuse, suggesting that the alterations are requisite for fusion or are an expression of a potentiality for fusion. The nature of these alterations and their exact role is unclear and may be species specific. Recent reports indicate that alterations, characterized by a flattening of cells, exist in the prefusion epithelium of developing human palates. The nature of these alterations and how they may be involved with shelf adherence and highly specific areas of fusion are unclear. A preliminary examination of the human palate with the scanning microscope has indicated that a striking surface alteration exists prior to fusion in those areas destined to fuse. It is the objective of this investigation to examine: the epithelium of the human palatal shelves prior to and during fusion in vitro and in vivo; the mechanism of shelf adherence and a characterization of the surface alterations and their role in the fusion process; the fate of surface alterations in isolated shelves. Specimens will be examined after collection in vivo and in vitro by scanning electron microscopy, transmission electron microscopy and the techniques of freeze cleavage and replication. Thus the purpose of this investigation is to elucidate the mechanism of fusion of the palatal shelves.